The present invention relates to a pressure adjusting valve, and in particular to a pressure adjusting valve for a variable capacity compressor to be mounted on air conditioners for vehicles.
Generally, a vapor compression type cooling system is extensively employed as a cooling system for a vehicle. According to this cooling system, a coolant is turned into a gas of high temperature and high pressure as the coolant is adiabatically compressed in a compressor, and this resultant gas is then liquefied as the heat thereof is released therefrom in a condenser. Thereafter, the resultant liquid is adiabatically expanded by means of an expansion valve thereby causing the liquid to absorb an external heat in an evaporator, thus causing the liquid to turn into gas while concurrently bringing about a cooling effect of air, the resultant gasified coolant being returned again to the compressor. Namely, this cooling system is a kind of refrigerating cycle which takes advantage of the heat of evaporation. FIG. 7 illustrates a refrigerating apparatus of the aforementioned vapor compression type cooling system, which is constituted by a compressor A, a condenser B, an expansion valve C and an evaporator D.
The compressor A shown in FIG. 7 is a reciprocating type compressor utilizing a wobble plate, and is consisted of a driving shaft 81, a wobble plate 82, connecting rods 83, pistons 84 and cylinders 85. The driving shaft 81 which is rotatably arranged inside a crankcase 80 is designed to be driven by an engine (not shown) through a pulley 86 and a belt 87 which are attached to one end of the driving shaft 81. The wobble plate 82 mounted on the driving shaft 81 is rotated following the rotation of driving shaft 81. The wobble plate 82 is spherically coupled, through an annular groove 88 formed in the wobble plate 82, with the connecting rod 83. On the other hand, the connecting rod 83 is coupled via a socket 89 with the piston 84, so that the connecting rod 83 and the piston 84 are permitted to be reciprocatively moved in conformity with an inclined state of the rotating wobble plate 82. Each cylinder 85 of the compressor A is provided with a suction chamber "s" and a discharging chamber "d" wherein these plural suction chambers "s" are mutually communicated with each other, and likewise, these plural discharging chambers "d" are mutually communicated with each other. The suction chamber "s" is provided with a valve which is designed to be opened in the suction stroke of the piston 84, while the discharging chamber "d" is provided with a valve which is designed to be opened in the discharge stroke of the piston 84. Further, the discharging chamber "d" is communicated with the condenser B, while the evaporator D is communicated with the suction chamber "s", so that a coolant discharged from the discharging chamber "d" is permitted pass through the condenser B, the expansion valve C and the evaporator D thereby bringing about a predetermined cooling effect, after which the coolant is returned to the suction chamber "s".
A pressure adjusting valve 1' is built in a suitable portion of the compressor A. This pressure adjusting valve 1' is designed to detect a pressure of coolant to be sucked in the cylinder 85 thereby altering the capacity of the coolant to be flown into the crankcase 80, thereby controlling the pressure inside the compressor A and hence to maintain the pressure inside the evaporator D. The suction chamber "s" of the cylinder 85 is communicated with a pressure chamber 21' of the pressure adjusting valve 1', the interior of the crankcase 80 is communicated with an intermediate chamber 22' of the pressure adjusting valve 1', and the discharging chamber "d" of the cylinder 85 is communicated with a valve chamber 23' of the pressure adjusting valve 1'. By the way, a escape passage for relieving the pressure inside the crankcase 80 is provided between the interior of the crankcase 80 and the suction chamber "s".
As shown in FIG. 8, this pressure adjusting valve 1' is constituted by a pressure responding motive portion 10' and a main body portion 20'. The pressure responding motive portion 10' attached to one end of the main body portion 20' comprises an upper lid 12' retaining a diaphragm 11' which is sandwiched between the upper lid 12' and a lower lid 22' integrally attached to the main body portion 20', and a case 13' which is integrally mounted through welding on the upper lid 12'. Inside this case 13', there are disposed an adjusting screw 17' screwed into the case 13', a spring shoe 15' contacted with an upper reinforcing plate 14' for the diaphragm 11', and a pressure-setting spring 16' interposed between the adjusting screw 17' and the spring shoe 15' and urging a ball valve 25' in the direction to open the passageway.
The main body portion 20' comprises an operating rod 24' contacted with a lower reinforcing plate 32' for the diaphragm 11', and a slide hole 28' formed passing through the main body portion 20'. A pressure chamber 21' is formed at a portion of the main body portion 20' where one end of the operating rod 24' and the lower reinforcing plate 32' are located, and is provided with an inlet port 29' for introducing a suction pressure (a suction pressure: Ps) of the cylinder 85. The other end of the operating rod 24' is extended to the valve chamber 23' in which there are disposed a ball valve 25' contacted with the other end of the operating rod 24', a valve seat 27', and a ball valve-retaining spring 26' interposed between a valve guard 33' contacted with the ball valve 25' and a spring shoe 46' built in the valve chamber 23', the ball valve-retaining spring 26' being set so as to urge the ball valve 25' in the direction to close the passageway.
A feeding port 30' for feeding a pressure (a pressure inside the crankcase: Pc) inside the compressor A is formed over the valve seat 27', and an inlet port 31' for introducing a discharge pressure (a discharge pressure: Pd) of the cylinder 85 is formed below the valve seat 27'. The pressure from the evaporator D is introduced into the suction chamber "s" and the pressure chamber 21', and when the suction pressure Ps is decreased, i.e. when the pressure inside the pressure chamber 21' is decreased, the urging force of the pressure-setting spring 16' becomes larger than the combined force of the diaphragm 11' and the ball valve-retaining spring 26', thereby causing the diaphragm 11' to move in the direction to push down the operating rod 24'. As a result, the ball valve 25' is opened, and the discharge pressure Pd is introduced via the pressure adjusting valve 1' into the interior of the crankcase 80, thereby increasing the pressure Pc inside the crankcase 80 and concurrently increasing the angle .theta. between the driving shaft 81 and the wobble plate 82, thus minimizing the magnitude of stroke of the piston 84.
On the other hand, when the pressure inside the pressure chamber 21' is increased, the urging force of the pressure-setting spring 16' becomes smaller than the combined force of the diaphragm 11' and the ball valve-retaining spring 26', thereby causing the diaphragm 11' to move in the direction to push up the operating rod 24'. As a result, the ball valve 25' is closed, thereby decreasing the angle .theta. between the driving shaft 81 and the wobble plate 82, thus enlarging the magnitude of stroke of the piston 84 (FIG. 7). Namely, the pressure adjusting valve 1' is designed to detect the suction pressure Ps and to control the pressure Pc inside the crankcase thereby to alter the magnitude of stroke of the piston 84, thus maintaining the pressure of the evaporator D.
It is desired that a vehicle is capable of suitably coping with any changes in operating environment, in particular, changes of environment due to atmospheric pressure and temperature. For example, the pressure responding motive portion 10' should be free from any influence by environmental changes as a vehicle travels on a road including a low altitude portion as well as a high altitude portion. With a view to cope with this problem, a pressure adjusting valve is proposed in Japanese Patent Unexamined Publication (Kokai) H5-39876 wherein the pressure-setting spring 16' is adjusted by means of a screw 17', and after a vacuum cap 18' is welded to the spring case 13', the pressure responding motive portion 10' is exhausted to a predetermined gas pressure or filled with an inert gas using a capillary tube (not shown) thereby preventing the pressure responding motive portion 10' from being influenced by changes in pressure and temperature (FIG. 8).
By the way, according to the aforementioned prior art, the diaphragm is held between the upper lid and the lower lid, and after the fringe portion of the diaphragm is welded, the spring case and capillary tube are secured to the upper lid by means of welding. Thereafter, the interior of the pressure responding motive portion is adjusted to a predetermined gas pressure, followed by the sealing of the capillary tube. However, the aforementioned prior art is accompanied with the problems that the reliability in air-tightness of the pressure responding motive portion may not be sufficient, since the air-tightness is effected only by the sealing of the capillary tube, and that since the manufacture of this pressure adjusting valve involves a large number of working steps and requires a large number of parts, the cost for manufacturing this pressure adjusting valve may be inevitably increased.